Method of measuring thickness of curved sections and apparatus therefor



Feb. 22, l949. 1 FRIEDMAN 2,462,088

METHOD 0F MEASURING THIGKNESS 0F GURVED SECTIONS AND APPARATUS THEREFORFiled Oct. 24, 1944 4 Sheets-Sheet 1 i:iil..

A\\\\\\\\\\ llllllllllllllllllll i'llll gmc/YM HERBERT FRIEDMAN Feb. 22,1949. H. FRIEDMAN 2,462,088

METHOD OF MEASURING THICKNESS OF CURVED SECTIONS AND APPARATUS THEREFORFiled Oct. 24, 1944 4 Sheds-Sheet 2 HERBERT FRIEDMAN Feb, '22,' 1949. H.FRIEDMAN 2,452,088

METHOD OF MEASURING THICKNESS OF CURVED SECTIONS AND APPARATUS THEREFORFiled Oct. 24, 1944 4 SheebS-Sheet 3 LIEEJE 3 MxLLnc-:RAMS oF RADIUMINTENSITY O 2 4 6 8 IO lI2 I4 I6 I8 2O 22 INCHES /32 rwmvto/v HERBERTFRIEDMN Feb 22 1949. H. FRIEDMAN y 2,462,088

METHOD OF MEASURING THICKNESS OF CURVED SECTIONS AND APPARATUS THEREFORFiled OCT.. 24, 1944 4 Sheets-Sheet 4 ILE-:.7

** SHEET COPPER ROLLED TO IO"DIAM CYLINDER -fuLEAD LINING ON INSIDE NOTBONDED TO COPPER 3 MILLIGRAMS OF RADIUM INTENSITY loo y so

I LEAD l 3.9" l

rgvlc/wto HERBERT FRIEDMAN Patented Feb. 22, 1949 UNITED smras Pn'rslvivOFFICE I'METHODOFJMEASURING THICKNESS 0F `CURVED SECTIONS ,'ANDJAPLBARATUS .THEREFOR vvHeribertaifr'ieaman, Arlington, va.

Application October/24, .1944;;Serial.No. v560,090 i (Cl. Z50- 83)kr(Grantedfunder the act of March 13,' 1883, amended April.f30, 1928;370 0. G. 757) '9 Claims.

lness. The \'di'iculty vinvolved in imaking.;v such fmeasurementsmechanicallyonllong'v sections of small ldiameter pipe yis 'toofapparentto need elaboration. VVhenitV isJdesired tocheckgtheunifiormity-l ofilined pipe or 'to :judge th'e.1 extentcof ffouling vof lpipe linesV--thef-"diiiiculties x of :mechani- "cal'fmeasurements 1-aremultiplied.y many `fold.

iRecently there have been proposed several methods of measuring'thicknesses of I' heavy'v steel :sections :andipip'e walls;whiohamethodseare all vbased on'measurementsvofbthe intensityofrtransmitted radiation and on the intensity of scattered radiation"compared-'mm1 Iincident radiation as disclosed, Ifor aexample,IiniUnitebl States Patent '2,277,756 :of Marchl, 1942, 11o-1D. 2G. AC.Hare, United States Patent 2,264,17 25 fof December 132, l1941 .to W.`E. l-Shoupp 4-and L. ';Tichvinsky, Unitedl/StatesfPatent 2,346,486 E ofApril `11, 11944 to D. -G. JC. -Hare fand/Unitedl States Patent2334.94'29 of Mayv 23, 1-9441to1G.-1Herzog :and` J. H. Stein.- Apparatuso'flthese 1 types l'have generally includedaj source of penetratingAradiation, such as vX-rays orl a1' radioactive fmateriaL: af detector,such as anfionization'chamberfor GeigerlMuller tube, andameasuringcircuit. Measurements'are based on, fthe exponential absorptionAlavv Ix'/Io=e/.f.px:in whichflouisfthe incident intensity, IIx' istransmittediintensity, ufthe=mass1absorption coelicientm the density ofthe irradiated'material `and thelengt'h'ofrthe raidiationjpath throughthefmaterial. While-measurements vbased* on'the measurement `of theabsolute "transmitted radiation intensity Aas vcompared YWith the`incident radiationintensity are satisfactory,.they involve severalinherent 'disadvantagesname1y,.thenom linearty .of fthe relationship',between `the transmittedintensity .and .the incident intensity,4inaccuraciesl in meter -andinstru-ment. .calibrations used indetermining the .fabsolute .intensities and the inconvenience eof lusngcalibration. data ',depending upon `rthe compositionofithe materialstudied.

A satisfactory method of measurement'based onsscatteringiof: back'radiation is :Wellndeseribed by Donald 16. C. :Harezin '.United;:States;:Ratent 2 l21,27'l'fZ5'61of Manch 31,l .11942,iwhichmeasurement falso follows a complex law, :namely k the Mcrosssection of the :incident beam; vk1 "a constantY dependent-on theelectron density Lof the material irradiated, `c'thel charge offanelecvtron, r'th'e distanceJfromo'the'1 scat-tering electron Vto thepointof"observation-mhe 'massfof the .,eleotron, "c thevelocityof'iight,lt the angle l"be- 'tweentheincidentand Lthe scattered Aray and-Xo the'thickness of the v`material irradiated. In `'theUnitedfiStatesiPatent2;349A29, V'Herzog andi-Stein disclose 'afmethodiof-measuring pipe wall thicknesses -baseil. r-on *the* irradiation of Jasegment of thepipe 'wall andfmeasurement of l'the intensity 'of thetransmitted radiation `intensity. "This ymethodyiike its npredecessors,f gives satisfactory results lout is' dependent upon "a -veryv lcomplexrelationship involving the "exponential absorp- `tion law 'and v`therelationshiploetvveenrtl'ieinner "an'd 'router i pipeyvall diameterandithe lengthof 'thepath"of'-radiation throughe thepipef'wall'vsegment.

It is the kprincipal object of 'fmy inventionrto provide a'methodofimeasuringthicknesses of curved elements, which need `notNnecessarily be uniformly curved,` using aradiation source Aand detectorin amannerWhicheliminates all direct depen'oleiice of' the* thickness@measurement-unime absolute intensity of the radiation transmittedkanllrtoi'base themeasurement^on a simple, direct, geometricfdetermination of the thickness It is the-'secondfobject 'of 'myinvention lto-provide an arrangement of apparatus -whereby -asimple-aand direotmeasurement of-pipearrclv tube wall thicknesses can beAmade Vffrom one side fof the pipeY using a mediation-source,-ladetectoraand calipers;

` It isfathird obj ect Aoffmy invention f* to provide a rapid'non-destructive l'-methodo'f inspecting Apipe and' tubingw forunformityrofswall r4thickness.

I`vinvention Y accordinglyV comprises the 'f-several steps varidftiie-relation -ofy one for' more `of such-stepsTtof-ea-eh of the othersfan'dthe lapparatus embodying lthe fcombinat-ionso'f elementsand-arrangements of parts-*Which arefadapted'y to eiect. such steps,all-ias exemplified in* thef'fllowiing'f'detailed disclosure and ythescope of 2thef invention -f will: beiindicate'd in the claims.

.The:rmethod.xandemeansrfor practicing-"my inventionfwilll' be7 more('clearly4 understood by'reference:toi:theiaccompanyingfdrawingsfiniwhioh,

Figure 1 is a diagram of one form of apparatus, partially in sectionshowing the arrangement of parts and their interrelationship;

Figure 2 is a detailed drawing of a part of the apparatus shown inFigure 1, and is a view taken along the line 2-2;

Figure 3 is a diagram of an apparatus used for inspecting pipe wallthicknesses;

Figure 4 is a detailed drawing of a part of the apparatus shown inFigure 3;

Figure 5 is a diagram of a simple intensity measuring circuitsatisfactory for use with the apparatus;

Figure 6 is a reproduction of data taken in measuring the wall thicknessof four-inch steel P11391 Figure 7 is a reproduction of the data takenin measuring the thicknessof ythe wall of aileadlined copper tube.

Briefly, my invention comprises a method and Q I'apparatus'ior detectingthe spatial relationship between the outside and inside walls of a pipeand a xed point by means of a iine pencil of radiation and detectorserving as indicators.

Referring to Figures 1 and 2 where a pre- Aferred form of apparatus forpracticing my invention isV illustrated; I represents a support ,onwhich various components of the measuring apparatus are mounted. Thissupport I0 is .usually a structure mounted over a work table `at aheight sufficient to permit sliding a pipe `under it on the same table.The table thus ,supports the support I0 and the pipe in fixed Irelation,to maintain which relation no clamps or chocks are necessary because ofthe fact that movement ofjthe beam throughl the pipe exerts nomechanical force thereon. A right and lefthand threaded arm II having adriving handle I2 is held at its ends by support I0. Arm II carriesthreaded members I3 and III which bear on angular member I5, suspendedfrom II) by .tension members II'Ia.

Member I shown in detail in Figure 2, is

V'guided in vertical motion relative to support.y

vI0 by lugs IB'and I'I and at its respective ends carries a radiationsource I8 and detector I9. .Member I5, as shown -in Figures 1 and 2, isa 'single piece bent to form the arms of an isosceles triangle. Itisslotted to permit its free move- V,ment in a Vertical direction relativeto arm II, and is bent at an angle which will be sufficient to span thelargest pipe section it is expected to measure.

Since it is desired-to produce and detect a fine pencil or narrow beamof radiation, source I8 is placed in a relatively deep hole in a leadblock to obtain a fine pencil of radiation. I have found-that a sourcecomprising a few milligrams of radium enclosed in a cylindrical platinumshell one centimeter long and one millimeter in diameter gives asatisfactory beam. To obviate` diiiiculty which would be created by thenormal divergence of the beam in passing from the source to the detectora collimating block 2| having `a hole aligned with source I8 is placedbefore detector I9. In the figure the relative size of the hole isexaggerated in order to simplify the mechanics of the showing. Thus, itwill be seen that the ends of member I5 are spanned by a very finepencil ofgradiation, or, rather, detector I9 is activated only by a veryfine pencil of radiation, which as' shown 'in Fig. 1 is horizontal andat right angles to the vertical radius of the pipe.

Al detail in the construction of the apparatus is shown in thearrangement of the detector. It is desirable to tilt detector I9 at aslight angle in order that a substantial part of the length of thecathode of the detector, which preferably is a Geiger-Muller counter,will be irradiated by the narrow beam of radiation coming through thecollimating hole in block 2I.

Detector I9 is electrically connected to a counting circuit having-itscomponents tube .22 and meter .23 mounted in housing 24. A commonform'of counting circuit used in Geiger- Muller tube circuits is shownin Figure 5.

The operation of the apparatus is relatively simple. It is Well knownthat the rapidity with which a Geiger-Muller tube will discharge dependsupon the number of quanta of radiation impinging upon it. As indicatedin the drawing, a ne pencil of radiation is directed at the detector I9.Interposition of any solid material between source I8 and detector I9results in the absorption of some radiation in the material and acorresponding decrease in the intensity of radiation reaching thedetector and associated measuring circuit. It is evident 'from the-igure that a pipe 25 interposed between source I8 and detector I9 andmoved vertically will interpose a solid metal path progressivelyincreasing in length between source I8 and detector I9 as indicated bypaths a, b, and c indicated by dotted lines in the drawing. A verticalmovement of the pipe upward beyond path a increases the effective solidpath traversed by the radiation beam. A vertical movevment of the pipeslightly beyond path c results in the sudden shortening of the effectivemetal path. The response of. the apparatus to vertical movement oi thepipe is a sudden decrease in received radiation intensity at thedetector when path a is passed and a sudden increase in receivedradiation intensity when path c is passed.

Inasmuch as it is usually inconvenient tot move a heavy pipe section,the apparatus itself can be madev to change the relative spatialpositions of the radiation path and the pipe wall. By turning handle I2,thus rotating arm II, riders I3 and I4 can be drawn together or pulledapart. Since riders I3 and I4 bear on member I5 which carries theradiation source and detector on its ends and member I5 is constrainedto move vertically as above described, turning of handle I2 has theeffect of moving the radiation beam vertically toward the center or awayfrom the center of the pipe while the latter rests upon the table uponwhich the support I0 is mounted thus maintaining the mutually orthogonalrelationship between the beam and the vertical radius of the pipe asshown in Fig. 1. The effect on the intensity of the radiation receivedby the detector is exactly the same as that produced by moving the pipe.

Thus it is clear that my method of measuring 'pipe wall thickness or thethickness of any greatest one=adecrease' andthe second an increase, in-

dicates the outer and inner boundaries of thel pipe"wallwrespectivelyl`ASince it is the outer andi'inrie'rwal-ls which-y are detected; it isVnot` A-good method of determining thicknessesofv curved1 sections is toplotwrelative intensity ofA received radiation versus the distance ther'a diation" beam is moved' as was done in Figures` 6 andi 7.In'FigureG, the thickness of thew'a'llof yif-inch steel `pipe wasmeasured according to thismethod; The measured wallI thicknessv ac'-cording to this method was 15.4/64 as compared with a thickness of /64determined by means of standard calipers. In Figure 7, results are givenas obtained with a lead-lined copperk tube on which' a measurement wasmade.

The 'gap between the unbonded lead and copper was detected clearly inthe measurement. Plotting of relative intensity of received radiationagainst movement of the beam permits close determination `of the wallthickness as the data of Figures 6 and '7 show. In both cases it isapparent that the precision of the determination could have'beenimproved by determination of a larger number of points near the criticalpoints of the curves,

In Figure 3 there is shown a design of a hand device for performingroutine inspections of pipe' walls to determine whether or not they arethick enough to satisfy requirements. In the drawing, 3|) represents arod-like support on Whichthe other parts of the apparatus are carried.At one end of the support there are mounted the radiation source |8 andholder 20 and at the other the detector |9`, block 2|, measuring circuithousing 24'; push-button (thumb operated) switch 3|, and handle 32through which pow-er cable 33 enters.

As was explained in connection with Figure 1', the eiective amount ofsolid interposed in the path of radiation will determine the intensityof that reaching the detector. In this apparatus, as explained inconjunction with Figure l, care is taken to providefor the detection ofa narrow pencil radiation' by providing collimatin-g block 2| andtilting detector I8.

Since the object in using this apparatus is to determine whether a pipeWall thickness exceeds a givenl minimum, no provision is made for movingthe beam radially past the wall. Wedges 34 and 35 together with bolt 36and lock nut 31 take the place ofthe micrometric movement of the beamshownin Figure 1.

In'Fgurjefl there is shown a detailed View of a wedge 34. As seen it hasa longitudinal slot to permit adjustment by means of nut and bolt 36 and31 of the separation between the head of bolt 36 and the line ofradiation.

In operation, wedges 34 and 35 are set by means of ilat headed bolt 36and nut 31 so that the path of the radiation through the metal pipe wallwill just equal the maximum path obtainable for the minimum acceptablepipe Wall thickness. To inspect a pipe, all that is required is to holdthe apparatus in the position shown, press activating switch 3|, andwait .a few seconds to get an equilibrium reading on the indicatingmeter, If the readings mamen;itzwnrindieatetosframasse tion. If thereading is substantiallylowertharrr expected for satisfactory pipeitwill indicate the presence of a thick spot in the pipe. The entirefypipe can be inspected-for' uniformity by'l sliding the instrumennslowly,longitudinally alongthepipe; y

Meter fluctuationsv willl indicate the locations of.

non=uniiormities in the pipe section. By rotatingl the pipe; whileholding the instrument in place;A

the cross vsections can be inspected also.

Inliigure 54 there-is shown a common formv of intensity measuringcircuit used. with Geiger--v Muller tubes. Itis not'the only type thatcan be' used, but is simple,V sensitive and notv subject tou erraticdeviationsffrom normal behavior. In the? g'ure |9 represents thedetector or Geiger-Mule high voltage source, which will be approximately1000 volts. The cathode is grounded through re-f sistance capacitancecircuit 50, 5|. itscontrol grid 52g connected to the' cathode of theGeiger-Muller tube. the 'tu-be; 3 represents theswitch of Figure y 3;.53 represents a meter andl 54 the power supply.

In operation, the charge on capacitor 5|`wl11-1.1l

be proportionalv to the frequency of discharge of Geiger-Muller tube|9iand willcontrol-the amount'.

of 4current flowing Vthrough the'tubel 52. Since the frequencyofdischargeof the Geiger-Mullen tube is proportional tothe intensity ofincident" radiation `and the intensity of. incident radiationv iscontrolled by the nature of the radiation path,

it is apparent that the indication of themeter 53`caniY-be made toindicate` the presence offso'liolf'i in the beam path.

From Vthe above description 'of my apparatus it is apparentthat mymethod of measuring' the thickness of a pipe wall rests upon a simplegeometric determination of the radial distance it is necessary to movethe radiation source` and detector-relative to the pipe wall to iind twosharp changes in intensityv of' received radiation. It

possesses the distinct advantages that:

No absoliite'dete'rmination of incident or trans-1 precise'determination:y of the ratio of' transmitted to incident radiationintensity is necessary; f

All errors caused by inaccuraciesin intensity measurements aresubstantially eliminatedV and all dependence is place'dupon a singlegeometric measurement by making the detector an 'indicator` rather thanythe primary scale;

The apparatus as disclosed canbe used to meas- A ure the wall thicknessof curved sections of any material; no separate calibrations fordiierent materials are required; it is not necessary that' the curvaturebe uniform since the separation of outer and inner wall is measured by ageometric determination;

The beam of radiation need not necessarily be directed through the pipewall in a direction perf pendicular to the pipeV axis since the outerand inner wall are located byfmovement of the beam.

ySince changes may be made in the practice of the above described methodand in the arrange- In the plate circuit of purposesiwithout the paymentof any royalties thereon or therefor.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1.lTh'e method of measuring the thickness of curved sections of solidmaterial by passing radiation into the curved surface in a direction toemerge through the same surface, comprising, arranging a source ofradiation and a detector so that the received radiation is a narrow beamnormal to a radius of curvature of the section, moving said radiationsource and detector toward the 'section while maintaining the beam ofradiation normal to a radius, detecting the beginning of decrease inintensity of received radiation at the detector and the beginning of itsincrease, the amount of motion of the source and detector between sharpchanges of received radiation intensity being a measure of the thicknessof the section.

2. The method of measuring the thickness of aV curvedsection of solidmaterial by passing radiation into the curved surface in a direction toemerge through the same surfacecomprising, maintaining the line ofradiation between a collimated beam of radiation and a detector and aradius of the section mutually orthogonal, causing relative motionbetween said section and said beam in the direction of said radius whilemaintaining said orthogonal relationship so that the amount of relativemotion between said section and beam of radiation occurring betweensharp changes in intensity of radiation received by the detector is ameasure of the thickness of the curved section.

3. The method of measuring the thickness of a pipe wall by passingradiation into the curved surface thereof in a direction to emergethrough the same surface, comprising, maintaining a mutually orthogonalrelationship between a radius of said pipe and a collimated beam ofpenetrating radiation while moving said beam radially toward the axis ofsaid pipe, and detecting sudden changes in the intensity of the beamincident upon a detector, said changes indicating the location of outerand inner boundaries of the pipe wall.

4. The method of measuring the thickness of a pipe wall by passingradiation into the curved surface thereof in a direction to emergethrough the same surface, comprising, maintaining a mutually orthogonalrelationship between a radius of said pipe and a collimated beam oflpenetrating radiation, while moving said pipe radially toward said beamand dectecting sharp changes in the intensity of the beam incident upona detector said changes indicating the outer and inner boundaries ofsaid pipe wall.

5. Apparatus for measuring pipe wall thicknesses by passing radiationinto the curved surface of said pipe wall in a direction to emergethrough the same surface, comprising, in combination, a source ofpenetrating radiation, a

8 highly collimated' beam detector therefor, means .for moving said beamthrough said pipe wall from the outside in a direction transverse to thebeam whereby to effect a slicing movement of the beam into the pipe andmeans for measuring the amount of motion of said beam.

A 6. Apparatus for measuring pipe wall thicknesses by passing radiationinto the curved surface of said pipe wall in a direction to emergethrough the same surface, comprising, in combination, a source of highlycollimated penetrating radiation, a detector therefor, means forproducing relative motion between said beam and said pipe moving theradiation beam toward the center or away from the center of the pipe,and means for measuring the amount of said motion.

7. Apparatus for measuring pipe wall thicknesses by passing radiationinto the curved surface of said pipe wall in a direction to emergethrough the same surface comprising, in combination, a source ofcollimated penetrating radiation, a Geiger-Muller tube arranged with ashield as a highly collimated beam detector therefor, a

measuring circuit for measuring and indicating the quantity of radiationreceived by said detector, and calibrated means for moving the radiationbeam toward or away from the center of the pipe.

8. Apparatus for inspecting pipe walls for uniformity of thickness bypassing radiation into the curved surface thereof in a direction toemerge through the same surface comprising a source of collimatedpenetrating radiation, a detector therefor and means for limiting theextent to which said pipe section can be interposed in said radiationpath so that the path of said -beam of radiation through a pipe of givenoutside diameter is a chord of constant length, independently of wallthickness.

9. Apparatus for measuring the thickness of curved sections by passingradiation into the curved surface in a direction to emerge through thesame surface, comprising, in combination, a source of penetratingradiation, a highly collimated beam detector therefor, means for movingsaid beam through said curved section from the outside toward the innerside and means for measuring the amount of motion of said beam.

HERBERT FRIEDMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,097,760 Failla Nov. 2, 19372,277,756 Hare Mar. 31, 1942 2,346,486 Hare Apr. 11, 1944 2,349,429Herzog May 23, 1944 2,370,163 Hare Feb. 27 ,1945

